A diffraction grating is an optical device with periodic structures such as grooves, the stuctures having dimensions within an order of magnitude of a wavelength of light. Gratings split and diffract an incident light beam into its constituent wavelengths and into several diffracted light beams traveling in different directions. Groove spacing density, depth and profile are some of the factors that affect the spectral range, efficiency, resolution and performance of the diffraction grating. For example, the spacing between grooves, together with the wavelength of the incident light, affects in part the directions of the diffracted light.
Diffraction gratings include reflection gratings and transmission gratings. A reflection type grating reflects incident light, thereby producing diffracted light on the same side of the grating surface as the incident light. In order to reflect an incident light, a reflection grating surface may have a reflective property applied through a reflective coating. A transmission type grating permits incident light to transmit through the grating surface, thereby producing diffracted light on the opposite side of the grating surface from the incident light, also known herein as behind the grating. In order to permit more incident light to transmit through the grating surface, a transmission grating surface may have an antireflective property by means such as an antireflective coating.
Diffraction gratings may be ruled or, holographic. A ruled grating may be produced by a ruling engine that cuts grooves into a grating substrate. A holographic grating may be produced by intersecting light beams that produce a holographic interference pattern on a grating substrate.